The present invention relates to a switchable mirror glass using a magnesium thin film or a magnesium-nickel alloy thin film (hereinafter collectively, xe2x80x9cmagnesium-containing thin filmxe2x80x9d), and, more specifically, the present invention relates to a novel switchable mirror material for use in a switchable glass capable of automatically controlling sunlight incident from a windowpane without a sunblind or curtain, a switchable mirror glass produced using the same material, and a method of controlling the same switchable mirror glass.
The present invention is a valuable material technology for controlling the light transmittance of a window in buildings or vehicles.
Generally, a great amount of heat comes in and out through windows (openings) in a building. For example, about 48% of heat from a heating system for winter flows out through windows, and about 71% of heat comes in an air-cooled room through windows in summer time. If the sunlight/heat transfer through windows is adequately controlled, an enormous amount of energy savings can be effectively achieved.
A switchable glass has been developed for the purpose of controlling the sunlight/heat transfer through windows.
There have been proposed various types of systems for controlling such a switchable glass. Among them, 1) a material having a light transmittance property reversibly changeable in response to current/voltage applied thereto is referred to as xe2x80x9celectrochromic materialxe2x80x9d, 2) a material having a light transmittance property changeable in response to the temperature thereof is referred to as xe2x80x9cthermochromic materialxe2x80x9d, and 3) a material having a light transmittance property changeable by controlling the state of atmospheric gas is referred to as xe2x80x9cgasochromic materialxe2x80x9d. Particularly, an electrochromic switchable glass using a tungsten trioxide thin film as a switchable layer has been extensively researched toward the practical use thereof, and some related products have already been placed on the market.
In principle, all of the conventional electrochromic switchable glasses are designed to control absorption level of incident light by the switchable layer such as a tungsten trioxide thin film. Thus, the switchable layer is inevitably heated as it absorbs the light, and the resulting heat will be reradiated toward a room, resulting in a deteriorated energy saving effect. To solve this problem, reflection level instead of absorption level of the incident light should be controlled. That is, it is desired to provide a material that can be reversibly changed between mirror and transparent states.
While it was quite difficult to discover such a material having a property reversibly changeable between mirror and transparent states, a research group in Holland discovered in 1996 that hydrides of rare earth metals, such as, yttrium or lanthanum, are reversibly changeable between mirror and transparent states in response to hydrogen. This material was named a xe2x80x9cswitchable mirrorxe2x80x9d (J. N. Huiberts, R. Griessen, J. H. Rector, J. R. Wijngaarden, J. P. Dekker, D. G. de Groot, N. J. Koeman, Nature 380 (1996) 231). While the rare earth hydrides have an excellent switchable mirror property of a large variation of light transmittance, the limited availability of rare earth materials and their hydrides, and high cost make it disadvantageous to use the switchable mirror as a coating of windows.
In 2001, a research group in the USA discovered a magnesium-nickel alloy Mg2Ni as a new switchable mirror material (T. J. Richardson, J. L. Slack, R. D. Armitage, R. Kostecki, B. Farangis, and M. D. Rubin, Appl. Phys. Lett. 78 (2001) 3047). Mg2Ni is expected to be a more suitable material for windowpane coatings because it is made of magnesium and nickel, which are more readily available and cost less than rare earth materials. Mg2Ni has a high reflectance in its mirror state, but a low visible light transmittance (20% from literature) in its transparent state. Thus, this material can be practically used only after the visible light transmittance in the transparent state is increased up to an adequate level.
Some materials are known to have the switchable mirror properties, such as hydrides of rare earth metal such as yttrium or lanthanum, rare earth-magnesium alloy hydrides, rare earth-gallium alloy hydrides, and magnesium-nickel alloy hydrides. Among them, the magnesium-nickel alloy hydrides are suitable as windowpane coatings in view of availability and cost. However, none of the previously reported magnesium-nickel alloys could be practically used due to their low light transmittance in their hydrogenated state. While the electrochromic switchable glass using a tungsten trioxide thin film has been extensively researched toward the practical use thereof, and some related products have already been placed on the market, as described above, the thin film has a complicated multilayer thin-film coating structure. This leads to extremely high cost which is a negative factor against promoting its use as a switchable window. Thus, there is still a strong need for new materials for a switchable glass with excellent properties and suitable for practical use.
Under the above circumstances, after extensive research on switchable properties of various compositions of magnesium and magnesium-nickel alloy thin films prepared through a sputtering method, the inventor found that (1) a magnesium thin film containing no nickel exhibits a specifically excellent switchable mirror property when it has a thickness less than a given value, (2) a film transparentized through hydrogenation exhibits a thermochromic property allowing the light transmittance of the film to be changed in response to its temperature, and (3) a new composition MgNix (0.1 less than x less than 0.3) has a significantly higher light transmittance in the transparent state than Mg2Ni. Based on these findings, the present invention was completed.
One object of the present invention is to provide a new type of switchable mirror material comprising a magnesium-containing thin film that is low in cost, and a catalyst layer containing, for example, a slight amount of palladium.
Another object of the present invention is to provide a switchable mirror glass window structure using the above switchable mirror material.
Still another object of the present invention is to provide a new switchable mirror material having a simple structure of two coating layers capable of facilitating cost reduction.
In order to achieve the above objects, according to a first aspect of the present invention, there is provided a switchable mirror material comprising (1) a magnesium thin film having a thickness of 40 nm or less, and preferably 10 to 20 nm, or a magnesium-nickel alloy thin film having an alloy composition represented by MgNix wherein 0.1 less than x less than 0.3, preferably, 0.16 less than x less than 0.2, (2) a transparent catalyst layer formed on a surface of the thin film, and optionally (3) a transparent protective layer formed on the catalyst layer. The switchable mirror material has a chromic property which allows the thin film to be switched from a mirror state into a transparent state by means of hydrogenation of the thin film, and to be switched from the transparent state into the mirror state by means of dehydrogenation of the thin film in a temperature range of about 20xc2x0 C. to 100xc2x0 C.
In the switchable mirror material in the first aspect of the present invention, the catalyst layer may be a palladium or platinum layer having a thickness in the range of 0.5 to 10 nm. The protective layer may be made of a hydrogen-permeable and water-impermeable material.
According to a second aspect of the present invention, there is provided a switchable mirror member comprising a transparent substrate, and a switchable layer including the switchable mirror material set forth in the first aspect of the present invention, wherein the switchable layer is formed on a surface of the transparent substrate.
In the switchable mirror member set forth in the second aspect of the present invention, the transparent substrate may be a transparent sheet made of acrylic or plastic material.
According to a third aspect of the present invention, there is provided a switchable mirror glass comprising a glass substrate, and a switchable layer including the switchable mirror material set forth in the first aspect of the present invention, wherein the switchable layer is formed on the glass substrate.
According to a fourth aspect of the present invention, there is provided a switchable mirror glass window which consists of double or triple glass plates. In this case, at least one of the glass plates is composed of the switchable mirror glass as set forth in the third aspect of the present invention with the switchable layer facing in the inward direction of the insulating glass structure.
In the switchable mirror glass window set forth in the fourth aspect of the present invention, the enclosed space between the glass plates is selectively supplied with either one of (1) hydrogen gas and (2) heated air or oxygen gas, from an atmospheric-state controller.
According to a fifth aspect of the present invention, there is provided a method of switching the states of a switchable mirror glass with a switchable layer including the switchable mirror material set forth in the first aspect of the present invention, by selectively causing hydrogenation and dehydrogenation in the switchable layer, in such a manner that the level of hydrogenation is selectively adjusted through at least one of a gasochromic process using hydrogen gas and an electrochromic process using electrolyte containing proton, and the level of dehydrogenation is selectively adjusted through at least one of a gasochromic process using air or oxygen gas, an electrochromic process using electrolyte and a thermochromic process based on heating.
According to a sixth aspect of the present invention, there is provided a method of switching the states of a switchable mirror member or glass with a switchable layer including the switchable mirror material set forth in the first aspect of the present invention, wherein the transition temperature of the magnesium thin film is set at any temperature in a given range in advance to allow the magnesium thin film to be automatically switched from the transparent state to the mirror state at the preset temperature in response to rise in atmospheric temperature.
In the method set forth in the sixth aspect of the present invention, the transition temperature may be set at any temperature in the range of about 20xc2x0 C. to 100xc2x0 C.
The transition temperature may be set depending on the thickness of the catalyst layer.
According to a seventh aspect of the present invention, there is provided a method of switching the states of a switchable mirror member or glass with a switchable layer including the switchable mirror material set forth in the first aspect of the present invention, wherein speed of dehydrogenation in the switchable layer is adjusted by controlling the temperature of air or oxygen gas to be supplied around the switchable layer. In this case, the level of dehydrogenation in the switchable layer to be varied according to the temperature of the air or oxygen gas may further be adjusted by controlling the thickness of the catalyst layer.
According to a eighth aspect of the present invention, there is provided an article comprising a switchable layer including the switchable mirror material set forth in the first aspect of the present invention, and either one of a switchable mirror glass and a switchable mirror member having a transparent substrate. The switchable layer is attached onto the surface of the switchable mirror glass or the transparent substrate.
The switchable mirror material having a magnesium-containing thin film or the switchable mirror glass using the switchable mirror material of the present invention has the following significant effects.
(1) The switchable mirror material of the present invention exhibits an excellent switchable mirror property far superior to the previously reported magnesium-nickel alloy Mg2Ni.
(2) The switchable layer having the magnesium-containing thin film can be advantageously applied onto the inward-facing surface of the switchable mirror glass used as at least one of the glass plates in the switchable mirror glass window having an insulating glass structure, for example a double glazing structure, to allow the states of the magnesium-containing thin film to be switched by introducing hydrogen gas and others into the enclosed space between the glass plates.
(3) The switchable mirror material can be prepared by using a low-cost metal such as magnesium and nickel, and a slight amount of catalytic material such as palladium coated on the thin film. Thus, the switchable mirror material is significantly advantageous in cost benefit terms.
(4) The switchable mirror glass can be effectively used as various window glasses for not only buildings but also vehicles including automobiles.
(5) The switchable mirror glass can be widely used in not only windows but also various kinds of articles, such as, shielding for privacy protection, ornamental articles or toys utilizing the feature of switching between mirror and transparent states, to add the switchable mirror function thereto.